Personalized mRNA vaccine slows melanoma recurrence in Phase 3 trial, Merck and Moderna say

Merck and Moderna said Wednesday that a personalized mRNA cancer vaccine, given together with the immunotherapy drug pembrolizumab, met its main goals in a large Phase 3 trial of patients with high-risk melanoma who had already had their tumors surgically removed. It is the first time an individualized cancer vaccine of this kind has succeeded in a Phase 3 trial, according to the companies and independent oncologists who reviewed the topline results.

The companies announced results from the trial, called INTerpath-001 and registered with the U.S. government as NCT05933577, which enrolled 1,137 patients with completely resected stage IIB–IV melanoma. Patients were randomly assigned, two to one, to receive either the vaccine, known as intismeran autogene, plus pembrolizumab (sold as Keytruda), or pembrolizumab alone for about a year following surgery.

What the trial found

An independent data monitoring committee determined, at a pre-planned interim analysis, that the combination produced "statistically significant and clinically meaningful improvements" over pembrolizumab alone on both the trial's primary endpoint, recurrence-free survival, and a key secondary endpoint, distant metastasis-free survival. The companies did not disclose the specific size of the benefit — such as a hazard ratio or percentage risk reduction — in the topline release, saying full data will be presented at an unspecified upcoming international medical meeting. No new safety concerns emerged, they said, with the side-effect profile consistent with earlier studies of the vaccine.

The result builds on an earlier, smaller Phase 2b trial called KEYNOTE-942, published previously, which found the combination cut the risk of recurrence or death by 49 percent and the risk of distant metastasis or death by 59 percent compared with pembrolizumab alone. Those numbers come from the earlier trial, not the new Phase 3 data, but they are the benchmark against which the new results will be judged once fuller figures are released.

How a vaccine gets built for one person

Intismeran autogene, also known by the laboratory designation mRNA-4157/V940, is not a conventional vaccine aimed at a pathogen shared by everyone. It is manufactured individually for each patient. After a tumor is surgically removed, researchers sequence both the cancerous and healthy tissue to identify mutations unique to that patient's cancer, then use an algorithm to select up to 34 of the resulting abnormal proteins, called neoantigens, most likely to trigger an immune response. Synthetic mRNA encoding those neoantigens is packaged into lipid nanoparticles — the same basic delivery technology used in Moderna's COVID-19 vaccine — and injected back into the patient, training the immune system to recognize and attack any cancer cells that carry those same mutations. Pembrolizumab, a checkpoint inhibitor already widely used in melanoma treatment, is designed to help the immune system sustain that attack.

"This is the first phase III study to show that intismeran, a treatment designed based on the unique mutational 'fingerprint' of a patient's own tumor, given in combination with pembrolizumab can reduce the risk of recurrence or death in patients with completely resected stage IIB–IV melanoma compared to pembrolizumab alone," said Georgina Long, the trial's principal investigator and medical director of the Melanoma Institute Australia.

Encouraging result, still an incomplete picture

Independent oncologists not involved in the trial, responding through the UK's Science Media Centre, described the result as a milestone while cautioning that key details are still missing. Marco Gerlinger, a professor of gastrointestinal cancer medicine at Barts Cancer Institute, called it "a breakthrough" and "the first phase 3 study that shows a vaccine can protect against recurrences." Lennard Lee, a consultant medical oncologist at the University of Oxford who advises the U.K. on cancer vaccines, said the findings were "significant" as the first positive Phase 3 trial of an individualized neoantigen therapy of any kind. Yin Wu, a Wellcome Trust fellow at King's College London, agreed the result was meaningful but noted that the exact size of the benefit, any increase in side effects, and the treatment's cost relative to its benefit all remain unknown until fuller data are published — factors that will determine how useful the vaccine ultimately proves in clinics.

Melanoma is the deadliest form of skin cancer, and while checkpoint inhibitors such as pembrolizumab have substantially improved survival for patients with resected high-risk disease over the past decade, a meaningful share of those patients still relapse. Earlier attempts to build therapeutic cancer vaccines against solid tumors have a long history of failure in late-stage trials, which is part of why oncologists are treating this result, cautiously, as a turning point rather than a formality. STAT News, reporting on the announcement, noted that a positive Phase 3 result had eluded personalized cancer vaccines until now.

What happens next

Merck and Moderna said they intend to present the full dataset at a major oncology meeting and to begin engaging regulators on a potential filing for approval of intismeran in combination with pembrolizumab. Dean Y. Li, president of Merck Research Laboratories, said the results "reinforce the promise of a more personalized approach to cancer treatment," while Moderna chief executive Stéphane Bancel said the companies were "helping turn that vision into a reality" for patients with few good options after a melanoma recurs. Detailed coverage of the trial design and endpoints has also begun circulating among oncology professionals through outlets such as the ASCO Post, ahead of the fuller data release. If the therapy is eventually approved, researchers say the same personalized platform could plausibly be adapted to other cancer types, though each would require its own trials to confirm any benefit.